Andrew B. Lassar is a Professor of Biological Chemistry and Molecular Pharmacology at Harvard Medical School. His research primarily focuses on understanding the transcriptional regulatory pathways that govern chondrocyte formation and maturation, as well as the mechanical loading effects on gene expression within joints. The Lassar lab aims to identify and characterize stem cell populations in articular cartilage, utilizing technologies such as genome-wide ATAC-Seq, ChIP-Seq, and RNA-Seq. Among their notable findings is the role of the transcription factor Sox9 in activating the chondrogenic differentiation program in mesenchymal cells. The lab's investigations have revealed Sox9's critical function in promoting the expression of chondrocyte differentiation markers, which is vital for endochondral ossification. Through lineage tracing, they have uncovered the distinct progenitor populations that contribute to articular and growth plate chondrocytes, highlighting the complex origins of these cells within the synovial joint. Lassar's work continues to seek factors that enhance Sox9-induced chondrogenesis and aims to restore articular cartilage stem cells in cases of joint degeneration.